Process for the manufacture of 3-ketals of polyketo steroids and products obtained thereby



United States Patent PROCESS FOR THE MANUFACTURE OF 3-KETALS OF POLYKETO STEROIDS AND PRODUCTS OB- TAINED THEREBY Eugene P. Oliveto, Bloomfield, and Emanuel l3. Hershburg, West Orange, N.J., assignors to Schering Corporation, Bloomfield, N.J., a corporation of New dersey No Drawing. Application .May 19, 1954 erialNo. 430,998

16 Claims. (Cl. law-239.55)

or groups can be regenerated, and to certain products obtained by such procedure. I

This application is a continuation-in-part of our copending application Serial No; 322,354, filed November 24, 1952, now U.S. Patent 2,773,888. I

It is the general object of the present invention to provide an improved procedure for the preparation of various 3-kato-hydroxy steroids and their esters and other functional derivatives from the .corresponding polyketo compounds.

A further object of the invention is to producenew 3-keto-hydroxy steroids and their functional derivatives which possess physiological activity or can serve as intermediates for the preparationof other compounds of therapeutic value.

A more specific object of the invention-isto convert -polyketo steroids wherein one. of the keto groups isin the 3-position, into 3-ketals, while the other keto group 'or groups remain free and socan be operated on to alter them chemically, or even to remove them, after which the S-keto groupcan be regenerated.

Other objects and advantages-of the invention will become apparent as the more detailed description thereof proceeds.

The 3-keto group is one of the more reactive of the keto groups present in steroid compounds, so that it is generally impossible to operate on the other keto groups without at the same time altering the 3-keto group. However, in many instances it is necessary to preserve, in the final product, the 3-ket0 group of the starting or of an intermediate compound. A procedure whereby the 3keto group is selectively blocked in the presence of one or more other keto groups, whereby such other keto groups can be chemically transformed, after which the 3-keto group can be easily regenerated, accordingly presents a highly advantageous and commercially valuable manipulation in the field of steroid synthesis.

We have found that in the presence of certain catalyststhe 3-keto group, provided that it is not conjugated to a double bond, can be selectively ketalized with alcohols and thereby protected against reagents employed to alter the remaining ket group or groups,provide d further that such reagents do not operate to "hydrolyze the 3-ketal .group. After the chemical operations on the free keto groups are comp1eted,"the ketalgroup is hyidrolyzed to regenerate the keto group. dBy such-procedure, entirely new keto compounds can' be' produced 2,927,921 Patented Mar. 8, 1960 2 which heretofore have baflied synthesis, while known compounds can be obtained in a simpler manner and/or in greater yield.

According to our invention, relatively stable ketals can be producedby reacting alcohols in the presence of an anhydride of a relatively weak inorganic acid with 3-keto steroids having one or more additional keto groups, there being nodouble bond in the 1,2 or 4,5- positions. The inorganic anhydride should be one which combines chemically with the water formed by the resulting ketalizatio'n, so that such water is removed from the reaction mixture and the reaction thereby caused to proceed in the desired direction. 'It may at this point be mentioned that while the invention is of particular advantage in the selective blocking of the 3-keto group of polyketo steroids, whereby chemical operations on the other keto groups are made possible without afiecting the S-keto group, it will be obvious that our. process is applicable also to 3'-keto steroids havingno other keto group but instead being susceptible at other points in the molecule, for example, to reduction, as for the saturation of nuclear double bonds in rings B, C and D, or the reduction of an ester group to an alcohol group, etc., which would cause simultaneous reduction, in whole or in part, of the 3-keto group were it left free. However, since the commercially'most valuable form of our invention at the present time is in connection with the selective. reduction ot certain keto groups of polyketo steroids while protecting the 3-keto group against reduction, the invention will be further described in connection with polyketo steroids ,(of which one keto group ,is always in the 3-position) and the chemicalconversion or elimination of keto, groups other than the 3-keto group.

While various inorganic anhydridescapable of stably binding the water that is liberated during the ketalization can be employed,'such as B 0 and S0 we have obtained best results with selenium dioxide (SeO and the most satisfactory embodiments of our invention will accordingly be'described with the use of such compound as the catalyst Also,although various alcohols can be employed for the manufacture ofthe corresponding ketals, such as benzyl and fi-phenethyl alcohols, we prefer .to employ the lower aliphatic alcohols (i.e. those having from 1 to 5 carbon atoms) and, in particular, methyl alcohol, which will accordingly be employed by way of illustration in the more detailed disclosure hereinafter. The primary alcohols arepreferred although some secondary alcohols can be utilized, like isobutyl alcohol.

found away to increase the yields of these ketal compounds by adding to the'reaction mixture (containing the steroid, an alcohol or glycol, and selenium dioxide) a small amount of a strong acid, eg, p-totuene sulfonic acid, benzene sulfonic acid, trichloracetic acid, or" per-,

-chloric acid. While in-such case the strong acid alone givesnone of the desired ketal, andselenium dioxide alone gives pooryields of the desired compound, the

mixture of the two gives excellent yields of 3-ketals containing substituents at positions 2 and/or 4. The strong acid may be present also during the ketalization of 3- keto steroids which are not substituted in the 2 and/or 4 positions, but generally will not then markedly affect the yield of ketal.

In carrying out our process, the polyketo steroid is reacted with the alcohol, preferably methanol, in the presence of a Selenium dioxide at room or at moderately elevated temperature to form the 3-ketal. The so formed ketal can then be subjected to a variety of reactions which may or may not involve the other keto groups present. Thus, the ketal can be pyrolyzed to yield a 3- methoxy-n -steroid, which can then be brominated to produce the 3-keto-4-bromo compound. Upon dehydrobromination, the A -unsaturation characteristic of cortisone and other steroid hormones can be produced. On

the other hand, the S-ketal can be reacted with a reducing agent to effect reduction of, for example, a ZO-keto group, after which the 3-keto group can be regenerated by acid hydrolysis. Where the less reactive ll-keto grouping is also present, a 20-keto group can be selectively reduced while the ll-keto remains unaffected; or, where the ll-keto is likewise reduced, it can be oxidized to a keto group, as with N-bromoacetarnide or other N-halogeno-acylamide, like N-bromosuccinimide after acylation of the ZO-hydroxyl with acetic, propionic, butyric, benzoic or other acid or anhydride.

Referring more particularly to specific reactions, we have found that pregnan-17a,21-diol-3,11,20-trione 21- acetate (1), reacted with methanol in the presence of selenium dioxide, yields the 3,3-dimethoxy ketal (II). Upon pyrolysis, methanol was eliminated from the ketal to yield 3-methoxy-A -pregnen-17a,21-diol-3,11,20-trione 21-acetate (III). The addition of bromine produced the known 4-bromopregnan-17a,21-diol-3,11,20-trione 21-acetate (IV), while dehydrobromination gave the unsaturated compound V.

Pregnan-17a-ol-3,11,20-trione (VI), pregnan-3,11,20- trione (XI) and pregnan-l1,B,17ct-diol-3,20-dione (XVII) all gave the corresponding 3,3-dimethoxy ketals upon reaction with selenium dioxide in methanol. These in turn were converted to the known 3,11-diketo 20,8-acetoxy compounds (X and XVI).

The final steps in the preparation of cortisone acetate (A -pregnen-17a,21-diol-3,11,2O-trione ZI-acetate) from bile acids comprise the bromination of pregnan-l7u,21- diol-3,11,20-trione ZI-acetate (I) in the 04 position (V. Mattox and E. C. Kendall, J. Biol. Chem., 185, 593 (1950)), followed by the elimination of hydrogen bromide and formation of the 4,5-double bond via the dinitrophenylhydrazone or semicarbazone (V. Mattox and E. C. Kendall, ibid., 188, 287 (1951); B. Koechlin, T. Kritchevsky and T. F. Gallagher, ibid., 184,393 (1950)), either of which ketone condensates may be converted to the 3-ketone by reaction with pyruvic acid (F. B. Hershberg, J. Org. Chem., 13, 542 (1948)).

In an attempt to find other routes which might lead to the introduction of the 4,5-double bond, we investigated the action of selenium dioxide on I. When a solution of I and selenium dioxide in methanol was warmed for a short time and then cooled, a new crystalline product deposited. Upon examination of the infra-red spectrum, the disappearance of one carbonyl group was disclosed, along with the appearance of a strong, saturated ether bond. Analytical data, plus the fact that this new compound could be easily reconverted to the starting material with aqueous acetic acid (or mineral acids), indicated that the compound was 3,3-dirnethoxypregnan-17a,21-diol,11,20- trione 21-acetate (II).

This unexpected reaction of selenium dioxide in methanol is probably the normal formation of a steroid ketal in which the selenium dioxide is functioning simultaneously as the acid catalyst andas the dehydrating agent, removing the water formed and thus driving the reaction to completion.

4 V V The dimethyl ketal, II, melted at about 180-190 C. with vigorous evolution of vapor, which apparently arose from the elimination of a molecule of methanol. When a sample was pyrolyzed at 200 C. for a short length of time, a new compound was obtained, M.P. 208-210, which was identified as 3-methoxy-A -pregnern17u,21- diol-11,20-dione 21-acetate, III, (methyl enol ether of 4,5- dihydrocortisone acetate) bymeans of analysis, infra-red spectrum, bromination experiments and hydrolysis to pregnan-17a,2l-diol-3,l1,20-trione 21-acetate. The high degree of stability of the ketol sidechain to this pyrolytic treatment was entirely unexpected.

The enol ether (III) readily added bromine in either methylene chloride or acetic acid solution to form 4- bromo-pregnan-17a,21-diol 3,11,20 trione 21 acetate (IV); the latter solvent gave a bromide with a somewhat higher rotation, and presumably a higher purity. Either bromide preparation could be readily converted to cortisone acetate (V) via the semicarbazone procedure.

The reaction of N-brornosuccinimide with coprostanone enol acetate has been reported (13. Armbrecht and M. Rubin, Abstracts of Papers, 119th Meeting of the American Chemical Society, April 1951) to give A -cholesten- 3-one directly. The first step was presumed to be allylic ibromination at C-5. However, when the same reaction was attempted with the enol ether III, a bromide was obtained which had an infra-red spectrum identical with that of the bromide obtained by the addition reaction and which was also converted to cortisone acetate by the standard procedure. Therefore the bromide from III must be 4-bromopregnan-1705,21-di0l-3,11,20-trione 21- acetate (IV) and not the 5-bromo compound which would be expected from allylic bromination. The 4-bromide may arise from either the addition of bromine or of N bromosuccinimide to the double bond, although the former is a more likely possibility especially in the light of the recent investigation (E. A. Braude and E. S. Waight, J. Chem. Soc. 1116 (1952) on the addition of bromine to ethylenic double bonds by using N-bromosuccinimide.

The structure of these ketals has been established by conversion to the known 3,11-diketo-20 8-1ydroxy compounds, isolated as the acetates (X and XVI). 3,3-dimethoxypregnan-l1,20-dione (XII) and 3,3-dirnethoxypregnan-l15,17a-diol-20-one (XIII) were reduced completely to the l1;3,20f3-dicls (XIII and XIX). After splitting the ketals with dilute acid, acetylation of the C-20 hydroxyl group and oxidation of the C-11 hydroxyl group, there were obtained the known pregnan-17ot,20/3- diol-3,l1-dione 20-acetate (X) and pregnan-ZOfi-ol-llldione ZO-acetate (XVI).

3,3-dimethoxypregnan-17m-ol-11,20-dione (VII) can be reduced partially with sodium borohydride to 3,3-dimethoxy-pregnan-17u,20}8-diol-1l-one (VIII). Hydrolysis of the ketal group, followed by acetylation at C-20, yields PICgHHH-t,20fl-dl0l-3,1l-dIOIlB ZO-acetate (X).

As already mentioned, the 3-keto group must not be conjugated to a nuclear double. bond; where such double .bond is present in the A-ring, the 3-ketal will not be formed. Thus cortisone acetate and A -androsten-3,17- dione failed to react. Keto groups at the 7,11,17 and 20- positions likewise failed to react, as in thecase of pregnan-3a-ol-ll,20-dione. It thus appears that keto groups which are conjugated to a double bond, or are joined to carbons at least one of which is tertiary, will not form ketals with alcohols in the presence of the catalysts above disclosed.

The reactions on the steroid compound following the ketalization should not be under such conditions as will cause hydrolysis of the ketal, at least not at a rate comparable to that of such reactions. Reduction at other points in the molecule is therefore preferably effected under neutral or alkaline conditions, as with alkali metal borohydrides and alkali metal aluminum hydrides (like sodium borohydride and lithium aluminum hydride), hy-

drogen in the presence of hydrogenation catalysts, etc. 1.

CH; CH: CH:

HO HO I HO 1 CHBO I CHaO I CHSO 011303 XIX XVII XVIII (1H3 (EH3 (3B3 CHOH CHOAO lCHOAC:

o Ii QOQ EIIQ odgy? In the above formulae, Ac stands for any suitable trated by the above formulae, but also to bile acids, acyl group, P ly Of a carboxylic acid, either androstanes, etiocholanes, sapogenins, pseudosapogenins aliphatic or aromatic Such as acetyl, propionyl butyryl and degraded sapogenlns having a 3-keto group, etc. Re-

. actions typical of bile acids are represented by the followe tz Phenacetyl cyclohexylawtyl benzoyl phthalyl 30 ing equations A and B, While those typical of androstanes are indicated by reactions and D, it being noted that The lllven'flon 1S applicable 3-keto Stemlds generally, the equation D illustrates the synthesis of estradiol from including not only the different types of pregnanes illusandrostane-dione:

C, O 7 l0 OH (1)11 I --0 OHaO l CHaO l I O Y 01180- 0330B 0 V D. 0 V (I) OH CF 0 CH O I o CHaO CHaO In the above formulae R stands for a hydrocarbon radical, such as lower alkyls, like methyl, ethyl and butyl,

or aromatic, like benzyl, or cycloaliphatic, like cyclohexyl and cyclopentyl, the methyl or ethyl radical being usually preferred.

As indicated in equations A and B above, the 3-keto group'of, for example, a 3,7-diketo steroid can be treated to remove the 7-ketonic oxygen (and/ or other ketonic oxygen, when present), as by the Woltf-Kishner reduction, for example, by conversion tothe semicarbazone followed by heating with sodium ethylate. As this reactionis well known, it has'not been thought to be necessary to illustrate it in detail.

-Our invention can be employed with compounds of both the normal and allo-series, and with compounds which are saturated or unsaturated in the B, C and D- rings.

The invention will be described in greater detail in the following examples which are presented only illustratively and not as indicating the scope of the invention.

EXAMPLE I (a) 3,3-dimethoxypregnan-1711,21 diol 11,20 dione- ZJ -acetate (lI).-A solution of 15.00 of pregnan-17u,21- dio1-3,11,20-trione-21-acetate (dihydrocortisone acetate, I) and 15.0 g. of selenium dioxide in 350 m1. of C.P. methanol was kept at 50-55 C. for 1 hour. The pre cipitate obtained upon cooling the solution. was collected with suction and after drying weighed 11.85 g., M.P. 179-215". Recrystallization from methanol gave two crops; 9.72 g., M.P. 193-195 with gas evolution and 1.45 .g. M.P. l84190 with gas evolution. An analytical sample, recrystallized again from methanol melted .at 181-184 with gas evolution, [A -+713 (acetone). "Analysis-Galen for C I-I O C, 66.64; H, 8.50. Found: C, 66.72; H, 8.80. Infra-red absorption studies showed the loss of a carbonyl group, and the appearance of the CO-C group.- V

(b) Hydrolysis of the 3,3-dimethyl ketal. A solution of 0.39 g. of II in 15 ml. of glacial acetic acid Was warmed on the steam bath to about 75, 15 ml. of water were added and the solution was allowed to stand overnight while cooling slowly to room temperature. 'The resulting crystals were collected, Washed and dried yield; 0.18 g., M.P. 230-234", [a] +81.31 (acetone); Dilution of the filtrate with water yielded an additional 0.15 g, M.P. 226229, [a] +83.34-. Total yield +94%. Neither fraction gave a melting point depression when mixed with dihydrocortisone acetate (I), and the infrared spectra were identical with that of dihydrocortisone acetate. 7

(c) 3-meth0xy-A -pregnen-1711,21 dial 11,20-dz'on'e 21-acetate (III).- A small flask containing 9.72 g. of (II) was heated gradually and with constant stirring in a Woods metal bath to a temperature of 200 over a period of about 30 minutes. f Upon cooling, the solidified residue was recrystallized from acetone to yield'4.70 g. (52%) of III, M.P. 208-210, [a] ]120.9 (acetone),

Anaylsis.Calcd for C I-1 C, 68.87; H, 8.19. Found: C, 68.91%; H, 8.51%. v

Hydrolysis of 0.50 g. of III as described for the 3,3- dimethoxy compound yielded 0.36 g, (75 M.P. 231-233". There was no depression in M.P. on admixture with dihydrocortisone acetate, and the infra-red spectrawere identical. v

(d) 4-br0mopregnan-17a,2] dial 3,11,20 trione 21- acetate (IV) (1) Bromination inmethylene chloride: A solution of 1.00 -g.of III in 40 ml. ofmethylene chloride was cooled in an ice bath and brominated by the dropwise addition of 0.40 g. ofbromine dissolved in 10 ml. of methylene chloride; Decolorization was instantaneous and copious fumes of hydrogen bromide were evolved. The solvent wasremoved under reduced pressure, leaving a residue which crystallized upon the additionof acetone. Re-

crystallization of this material from aqueous acetone gave (2) Bromination in acetic acid: A solution of 0.50 g. of III in 10 ml. of glacial acetic acid at 25 C. was brominated by the drop-wise addition of 0.20 g. of bromine in 4 m1. of acetic acid. Fumes. of hydrogen bromide were again evolved. The solution was poured into water and the solid was collected on a filter and washed with water. Recrystallization from aqueous acetone gave 0.35 g. of IV, M.P. 184-186 d., 1] {9l.4-" (acetone).

Analysis.-Calcd for C H O Br: Br, 16.53; Found: Br, 16.61%.

(3) Bromination with N-bromosuccinimide: A suspension of 1.00 g. of III in 100 ml. of carbon tetrachloride was heated to reflux. The addition of 0.45 g. of N- bromosuccinimide caused most of the solid to dissolve within 5 minutes and reflux was continued'25 minutes longer. The solution was cooled, chilled and the resulting solid collected with suction, washed with water and dried. Recrystallization from aqueous acetone gave 0.46 g., [e +1O5.l (acetone). 7

(e) Cortisone acetate V.-The bromides were put.

through the semi-carbazone formation and split as de scribed in the literature:

I V.'Mattox and E. C. Kendalhlournallof Biological Chem I istry, 188, 287 (1951); B; Koechlin, T. Kritchevsky aud'T." Gallagher, ibid., 184,393 (1950 All rotations were in dioxane and the u.v. determinations in ethanol. The crude cortisone acetate (V) was crystallized from aqueous acetone. Infra-red spectra showed no significant differences between the three samples and a reference sample of cortisone acetate.

EXAMPLE 2 (a) 3,3 dimethoxyp regn a n 11 ,170. dial 20- one (X VIII ).-A solution of 5.00 g. of pregnan-11B,17a-diol- 3,20-dione and 5.0 'g. of selenium dioxide in ml. of

C.P. methanol was kept at 50 C. for 2 hours and atroom temperature (30) for four hours. No crystals formed, whereupon a solution of 5 g. of potassium-bydroxide in GP. methanol was. added and the alkaline 11 solution was poured into water. The precipitated solid was collected with suction, washed with water and dried; weight 4.56 g. Recrystallization from ether-hexane gave two crops of XVIII, 3.95 g., M.P. 164-168 with gas evolution, and 0.44 g., M.P. 156-159 with gas evolution. A sample recrystallized for analysis melted at 168-171 dec., [u] +23.5 (chloroform).

Analysis.Calcd for C H O C, 70.01; H, 9.71. Found: C, 70.06; H, 9.81.

(b) Pregnan 11621701305 trial 3 one 20-acetate (XXI ).-A solution of 3.92 g. of 3,3-dimethoxypregnan- 11,8,17a-dll-20-0I16 (XVIII) in 100 ml. of C.P. methanol containing 0.4 g. of potassium hydroxide was combined with a solution of 4.00 g. of sodium borohydride in 10 ml. of water. After refluxing for 16 hours, the solution was diluted with water and extracted three times with methylene chloride. The combined extracts were washed twice with water, dried over sodium sulfate, and evaporated, leaving a colorless oil. In order to hydrolyze the dimethoxy group, this residue was taken up in, 20 ml. of acetic acid, treated with 20 ml. of hot water and heated for 15 minutes on the steam bath. After cooling, the solution was diluted with water and extracted with methylene chloride. The extracts were washed with dilute sodium bicarbonate solution and water, dried over sodium sulfate, and evaporated. The residue, again an oil, was acetylated by treating with acetic anhydricle in pyridine over-night at room temperature. The solution was diluted with water and extracted with methylene chloride. The extracts were washed with water, dilute hydrochloric acid, water, dilute sodium bicarbonate solution, and water. Drying over sodium sulfate and evaporation left 3.45 g. of crystalline material. Recrystallization from acetone gave two crops: 1.57 g., M.P. 248-250 and 0.43 g., M.P. 239-24l. A second crystallization-oi the first crop gave 1.44 g. of product, M.P. 250-252", [a] +63.0(chloroform).

Analysis.-Calcd for C H O C, 70.37; H, 9.25. Found: C, 70.76; H, 9.53.

(a) 3,3 dimethoxypregnan-l7a-0l-IJ,20-di0ne (VH). A solution of 2.00 g. of pregnan-17a-ol-3,l1,20-trione (VI) and 2.00 g. of selenium dioxide dissolved in 80 ml. of C.P. methanol was allowed to stand 2 days at room temperature. addition of a methanolic solution of 3 g. of potassium hydroxide and poured into water. After filtration and drying, the crude product weighed 1.87 g. The material was recrystallized from ether-hexane (in the presence of a few drops of pyridine), and gave 1.35 g. of VII, M.P. 138-l41 with bubbling. Another crystallization raised the M.P. to 148-150" dec., [a] +35.0 (chloroform).

Anaylsis.-Calcd for C H O Found: C, 70.25; H, 9.41. V

(b) Pregnan 17a,20B-di0Z-3,1Z-di0ne-20-acetate (X). -(1) A solution of 1.20 g. of 3,3-dimethoxypregnan- 17a-ol-l1,20-dione (VII) in 40 ml. of C.P. methanol was added to a solution of 1.2 g. of sodium borohydride in 4 ml. of water, the mixture allowed to stand at room temperature (24) for three hours, and then worked up as before. Hydrolysis of the dimethoxy group followed by acetylation, as described above, yielded 1.17 g., M.P. 183-190. Recrystallization from ethanol gave two crops: 0.61 g., M.P. 215-222 and 0.06 g., M.P. 251- 253". A mixed M.P. of the second crop with pregnan- 1lfi,17a,20/3-triol-3-one-20-acetate (Xa) showed no depression, and the infra-red spectra were identical. A second crystallization of the first crop yielded 0.52 g. of X solvated with ethanol, M.P. 222-224, [oz] +59.5 (acetone). Reported M.P. ZZZ-224. (L. H. .Sarett, Journal of Biological Chemistry 71,1169 (1949)).

Analysis.Calcd for (32311 3405; C2H5OH: C, H, 9.23. Found: C, 68.66; H, 9.61.

(2) A solution of 0.50 g. of pregnan-l1fi,17a,205-triol- The solution was made alkaline by the 12 3-one-20-acetate (Xa) in 75 ml. of C.P. acetone and 7.5 ml. of water was cooled to 3 and treated with 0.35 g. of N-bromo-acetamide. After 18 hours at 3, a solution of 1 g. of sodium sulfite in a minimum amount of Water was added and the acetone was removed under reduced pressure. The concentrated suspension was diluted with water and the solid collected with suction weighed 0.48 g., M.P. 218-220. Recrystallization from ethanol gave 0.42 g., M.P. 223-225 [a] +59.6 (acetone). A mixture M.P. with the sample prepared in 1) showed no depresion. Y t

EXAMPLE 4 (a) 3,3 dimethoxy-pregnan-I1,20-di0ne (XII). A solution of 1.00 g. of pregnan-3,11,20-trione (X1) in 40 ml. of C.P. methanol was treated with 1.00 g. of selenium dioxide and allowed to stand 2 days at room temperature. The solution was made alkaline by. the addition of 1 g. of potassium hydroxide in methanol, and poured into water. Filtration yielded 0.85 g. of material melting at 136-143. Recrystallization from hexane gave 0.75 g., M.P. 140-142", [a] +l30.4 (chloroform).

Analysis.--Calcd for C H O C, 73.36; H, 9.64. Found: C, 73.48; H, 9.85.

(b) Pregnan-20fi-0l-3,1I-dione-ZO-acetate (XVI). A solution of 1.70 g. of 3,3-dimethoxy-pregnan-l1,20- dione in ml. of C.P. methanol containing 0.2 g. of potassium hydroxide was added to a solution of 3.40 g. of sodium borohydride in 8 ml. of water. After refluxing for 16 hours, the solution was cooled and worked up as previously described. The dimethoxy group was hydrolyzed by treatment with 50% acetic acid and the residue was acetylated, again as previously described in the formation of X. This material was taken up in ml. of C.P. acetone and 20 ml. of water. The solution was cooled to 3 and 1.78 g. of N-bromoacetamide was added. After 3 hours at 3", the solution was poured into 1 liter of water containing 3 g. of sodium sulfite. Filtration yielded 1.43 g. of solid melting at ISO-170. This material was taken up in C.P. benzene and chromatographed on 17 g. of Florisil (100/200 mesh). Elution with benzene gave 0.96 g. of material, M.P. -1989. Two recrystallizations from methanol yielded 0.49 g., M.P. 201-203, [a] +66.6 (acetone). Reported M.P.. 201-203 (L. K. Sarett, ibid., 71, 1165 (1949)).

Analysis.Calcd for C H O C, 73.76; H, 9.15. Found: C, 73.56; H, 9.45.

EXAMPLE 5 Androstan-J 7 B-ol-3-bne A solution of 1.0 g. of 3,17-androstandione in 50 ml. of methanol and containing 1 g. of selenium dioxide, was. allowed to remain in an ice-chest overnight. The formed 3,3-dimethoxy-androstan-17-one was not-separated. One gram of solid potassium hydroxide and 2.5 g. of sodium borohydride in 2.5 ml. of water were added and the mixture allowed to react at room temperature for 24 hours.

The solution was then poured into a large excess of EXAMPLE 6 E tiocholan-I 15,17fl-di0l-3-0ne In a manner similar to Example 5, 1 g. of etiocholan- 3,11,17-trione was treated with selenium dioxide in methanol to give the 3,3-dimethyl ketal. This was not isolated, but reduced with sodium borohydride and potas sium hydroxide to yield the corresponding 1113,17fi-diol.

' Found: C, 70.26; H, 9.67.

EXAMPLE 7.

A mixture of 10.0 g. of pregnan llfl,l7u-diol-3,20- dione, 10.0 g. of selenium dioxide, 150 ml. of ethylene glycol and 100 ml. of alcohol-free chloroform, was stir red for 24 hours at room temperature. The reaction mixture was poured into a solution of 20 g. of potassium carbonate in 1.5 1'. of water and extracted with methylene chloride. The extract was washed withwater, driedwith magnesium sulfate and upon evaporation left a solid residue weighing 11.06 g., M.P. 225-2299. The analytical sample of pregnan-llfl,17a-diol-3,20-dine 3-ethylene ketal, crystallized from acetone-hexane, melted at 232.4- 233.8.

Analysis.--Calcd. for C H O C, 70.307; H, 9.24.

' EXAMPLE 8 4-bromopregnan-11BJ7o -di0l-3,20-dione 3-ethylene ketal (a) When 1.0 g; 'of 4-bromopregnan-l113,17u-diol-3,20- dione was treated with ethylene glycol and selenium dioxide as in Example 4(a), only a small amount c13 4- bromopregnan-l1B,17a-diol-3,20-dione 3-ethylene ketal was obtained. Even lengthening the time of reaction to six days did not substantially improve the yield.

(b) A mixture of 1.0 g. of 4bromopregnan-11 9,17udiol-3,20-dione, 1.0 g. of selenium dioxide, 0.1 got ptoluene sulfonic acid monohydrate, ml. of ethylene glycol and 25 ml. of alcohol-free chloroform was stirred at 25 for four days. Methylene chloride was added and the organic layer was washed with water, dilute sodium bicarbonate solution, water, and dried over magnesium sulfate. The solvent was removed by distillation and the residue triturated with ether. There was obtained 0.6 g. of 4-bromopregnan-11p,17u-dio1-3,20-dione 3- ethylene ketal M.P. 178-179 dec. r 1

Variations from the specific procedures hereinabove disclosed may be resorted to by those skilled in the art within the scope of the appended claims without departing from the spirit of the invention.

We claim:

1. Process for the selective protection of the 3-keto group of a polyketo steroid of the class consisting of (1) 3-keto-pregnanes having an additional keto group in at least one of the 7-, and 11-, and 20-positions, (2) 3- keto-androstanes having an additional keto group in at least one of the 11- and 17-positions, and (3) 3-keto etiocholanes having an additional keto group in at least 1 one of the 7- and l2-positions, the S-keto group being in each case in a non-conjugated relation to a double bond, which comprises reacting such steroid under substantially anhydrous conditions with a saturated lower aliphatic alcohol in the presence of selenium dioxide and of a strong acid, to form the 3-ketal.

2. Process according to claim 1, wherein the alcohol is primary.

3. Process according to claim 1, wherein the alcohol is methyl alcohol.

4. Process according to claim 1, wherein the steroid is a 3,20-diketo pregnane having a keto group also in one of the 7- and ll-positions. d

'5. Process according to claim 1, wherein the steroid is a 3,20-diketo-4-bromo-pregnane, and wherein the acid is p-toluenesulfonic acid.

6. Process according to claim 1, wherein the aliphatic alcohol is ethylene glycol.

mine and iodine. V

8. Process according to claim 1, wherein the steroid is a 3,20-diketo pregnane.

9. 3-ethylene ketal of pregnan-l1B,17a-diol-3,20-dione. 10. Process for the manufacture of 3'-ketals of a 3,20- diketo-pregnane, while leaving the 20-keto group unre acted, which comprises'reacting a 3,20-diketo pregnane wherein the 3-keto group is non-conjugated to a double bond, with a lower aliphatic alcohol in the presence of selenium dioxide and of a strong acid.

- 11. Process for the manufacture of 3-ketals of a 3,20- diketo-pregnane, while leaving the 20-keto group unreacted, which comprises reacting a 3,20-diketo pregnane wherein the 3-keto group is non-conjugated to a double bond, with ethylene glycol in the presence of selenium dioxide and of a strong acid.

12. A 3-ethylene glycol ketal of a 3,20-diketo-pregnane having a saturated A-ring, the 20-keto group being free. 13. A 3-lower alkylene ketal of a 3,20-dilceto-pregnane having a saturated A-ring, the 20-keto group being free.

14. A 15.-lower aliphatic alcohol ketal of a 3,20-diketopregnanehaving a saturated A-ring, the 20-keto group of I said ketal being free, and said ketal having attached to at least one of the 2- and 4-carbons a member of the References Cited in the file of this patent UNITED STATES PATENTS 2,294,433 westphal Sept. 1, 1942 2,647,134 Hogg July 28, 1953 2,656,367 Graber Oct. 20, 1953 2,666,068 Hanze Jan. 12, 1954 

1. PROCESS FOR THE SELECTIVE PROTECTION OF THE 3-KETO GROUP OF A POLYKETO STEROID OF THE CLASS CONSISTING OF (1) 3-KETO-PREGNANES HAVING AN ADDITIONAL KETO GROUP IN AT LEAST ONE OF THE 7-, AND 11-, AND 20-POSITIONS, (2) 3KETO-ANDROSTANES HAVING AN ADDITIONAL KETO GROUP IN AT LEAST ONE OF THE 11- AND 17-POSITIONS, AND (3) 3-KETO ETIOCHOLANES HAVING AN ADDITIONAL KETO GROUP IN AT LEAST ONE OF THE 7- AND 12-POSITIONS, THE 3-KETO GROUP BEING IN EACH CASE IN A NON-CONJUGATED RELATION TO A DOUBLE BOND, WHICH COMPRISES REACTING SUCH STEROID UNDER SUBSTANTIALLY ANHYDROUS CONDITIONS WITH A SATURATED LOWER ALIPHATIC ALCOHOL IN THE PRESENCE OF SELENIUM DIOXIDE AND OF A STRONG ACID, TO FORM THE 3-KETAL.
 12. A 3-ETHYLENE GLYCOL KETAL OF A 3,20-DIKETO-PREGNANE HAVING A SATURATED A-RING, THE 20-KETO GROUP BEING FREE. 